In the past, and at present, known methods of inserting an optical elements in-line with on optical fiber have been difficult and costly. Elements such as optical absorption filters, dielectric filters or mirrors, birefringement or polarization elements, saturable absorbers, light modulators as well as other elements can be inserted into an optical fiber. One common method of in-line insertion of elements requires cutting an optical fiber, polishing both cut ends of the fiber, and installing lenses to direct a beam coming out of one lens into the other. In operation, a collimated beam coming out of one end of the fiber propagates in free space and is focused by the other lens back into the second end of the optical fiber. An optical element is inserted into the space between the lenses as required. There are several disadvantages to his method. There is a high insertion loss due to the fact that much of the transmitted light is unguided; the arrangement is complex and is very sensitive to alignment; the beam diameter in the space between the lenses is large, therefore, the device is not suitable for non-linear applications.
In an attempt to overcome many of these disadvantages, S. Matsui et al. in Opt. 31, p. 1252, 1992 describe a technique for in-line insertion of a thin-plate optical element. The element is inserted into a precise narrow groove, cut across the fiber. This technique obviates most of the problems associated with a collimated beam device, however, it requires complex and expensive tools for cutting the narrow groove with micrometer accuracy.
U.S. Pat. No. 5,082,345 in the name of Cammons et al. issued Jan. 21, 1992, discloses an optical fiber connecting device including an attenuator element. Cammons discloses a cylindrical type optical fiber connector which includes an attenuator element that is capable of movement during the assembly of the connector. The connector includes a cylindrically shaped sleeve which has a longitudinally extending slot formed through the wall thereof. The attenuator element includes a rail comprising a head and neck which provides a path for the element to be moved by sliding along the slot in the ferrule sleeve of the connector which is parallel to the fiber axis. Cammons' attenuator arrangement requires that the connector coupling housing provide clearance for the attenuator support rail to ride in the slot of the sleeve. Although Cammons invention appears to perform its intended function, the arrangement is somewhat complex and is dependent on the type of optical connector used. The disk-like attenuator element must be shaped to have a rail which conforms to, slides within, and is supported by the slot and furthermore, the connector itself must have such a slot. Cammons' invention would not be suitable for use with many types of optical connectors.
It is therefore an object of this invention to provide a simple inexpensive method for in-line insertion of optical elements which obviates the aforementioned disadvantages.